1. Field
The present disclosure relates generally to “Completely Automated Public Turing test to tell Computers and Humans Apart” (hereinafter “CAPTCHA”). More specifically, the present disclosure relates to a technique for making CAPTCHAs selectable.
2. Related Art
A CAPTCHA is a test that is easy for a human to pass, but difficult for a machine to pass. For example, a CAPTCHA might involve typing a word that is presented in a visually noisy way such as by distorting the word, placing it on a textured background, and overlaying it with randomly placed line segments of varying thickness. Machines have long been able to recognize words, but such visual noise makes this recognition task difficult for machines. In contrast, most humans do not have difficulty recognizing words, despite visual noise.
CAPTCHAs are useful in many online applications. For example, CAPTCHAs can help prevent computer-automated robots (“bots”) from taking online polls, creating new email accounts, and causing fraudulent advertising clicks. Bot programs can produce e-mail accounts that are difficult to trace, making them ideal vehicles for proliferating spam. Bots can also infiltrate chat rooms; collecting personal information and posting links to promotional sites; generate worms; break password systems; invade privacy; and generally drain resources.
To defend e-commerce systems from bots, an increasing number of companies are securing their sites with CAPTCHAs. For example, users registering on Yahoo must first correctly recognize a distorted word displayed against a cluttered background and then type the word in order to prove they are human.
Advances in automated techniques for solving CAPTCHAs have led to the creation of CAPTCHAs that are harder for bots to solve. Current CAPTCHAs have become sufficiently difficult for humans to solve that many service providers now balk at deploying them for fear of deterring potential clients. This has made CAPTCHAs somewhat annoying, time-consuming, and difficult to use, particularly on devices with a limited user interface.
One way to reduce the annoyance and difficulty of use of a CAPTCHA is to present images of objects and let the user select those images that have certain properties. For example, ASIRRA, a CAPTCHA system developed by Microsoft, uses a CAPTCHA challenge involving identifying all the cats in a sequence of twelve images of both cats and dogs. Note that ASIRRA is based on images of pets rather than on an alphanumeric sequence. This is an important distinction because recent evidence suggests that a machine might be able to easily discriminate between images of dogs and images of cats. In contrast, passing a CAPTCHA challenge based on an alphanumeric sequence has been shown to be difficult for a machine. This is because an alphanumeric sequence can be distorted and made noisy in such a way that a person with a required skill can pass the CAPTCHA challenge, but a machine cannot. In contrast, distorting an image of a dog or a cat might simply make it unrecognizable for both humans and machines.
For example, passing a CAPTCHA challenge on a mobile device is more cumbersome and time-consuming than with a traditional keyboard. Therefore, a test to distinguish humans from computers that can be solved more easily on a mobile device would be far less distracting and more acceptable to most users.